The above mentioned applications describe an improved microcomputer comprising a single integrated circuit device having a processor and memory in the form of RAM on the same integrated circuit device, the processor being arranged to operate in accordance with functions selected from a function set. Said function set includes direct functions and indirect functions, the indirect functions being used to select one of a variety of "operations". Said operations include the operation "synchronise" which is used to permit two processes to communicate with each other, the two processes being either on the same microcomputer or in other cases the two processes may be on separate respective microcomputers. As can be seen from the above mentioned patent applications, use of the operation "synchronise" has required two word locations in memory to provide a channel permitting process to process communication on the same microcomputer. One word of the channel was used to indicate the state of the channel and the other word was used to hold data for communication through the channel. Furthermore, process to process communication requires that each process includes in its program sequence two operations of "synchronise" for each message transmission in order to ensure that the message transmission occurs when the two processes are at corresponding stages in their program sequences. In some circumstances this may cause a process to be descheduled twice in order to effect synchronised message transmission.